Siemens-Martin open-hearth process

Siemens-Martin open-hearth process is an obsolete process for making steel in which streams of air and fuel gas were fed alternately onto the furnace
contents. It was used to make most of the steel during the twentieth century
but was then superseded by the basic oxygen and electric-arc
methods. The open-hearth process used the gases from the molten charge
to pre-heat the air blast and so economize on fuel. An alkaline lining was
used if the ore contained phosphorus.